[ovirt-devel] migration enhancements feature

[Yaniv Kaul]

On Mon, Sep 14, 2015 at 3:35 PM, Tomas Jelinek <tjelinek at redhat.com> wrote:
> Hi all,
>
> there is an effort for enhancing the speed and convergence of the migrations (especially for large VMs).
>
> The feature page targeted for 4.0 is [1].
>
> TL;DR:
> - remove current logic from VDSM and move to engine in form of policies
> - employ post-copy migration
> - employ traffic shaping
> - protect destination VDSM against migration storms
>
> Any comments more than welcome!
> Tomas
>
> [1]: http://www.ovirt.org/Features/Migration_Enhancements

I think we need to look at (any/the) feature from the user
perspective, first and foremost. How would the user use the feature?
What 'knobs' he may tweak to get better migration results? Which can
we do for him? Which ones will be used on the expense of others?
Do we truly believe a user will know what to tweak to get a better
result? Exposing every parameter, in that sense, is
counter-productive.

Specific example: should a user enable or not compression? What will
he gain? I assume, less bandwidth needed for migration. Would it help
for his migration (I assume it'll take longer, take more CPU, etc.) or
not? When migrating one big heavily-used VM? When migrating twenty
idle single-core VMs? Any point enabling it for 10Gb dedicated
migration network? And 1Gb shared network which is heavily used by
others? etc.

Y.

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